Doctors are looking for more information about a “polio-like syndrome” that has caused paralysis in a few children in California.

Neurologists have identified five patients who developed paralysis in one or more of their limbs between August 2012 and July 2013.

All five children had been vaccinated against the poliovirus.

Treatment did not seem to help the children regain their motor function.

Samples from two of the children tested positive for enterovirus 68, a rare virus that has been linked to severe respiratory illness in the past.

Samples from the other three children were not collected or tested soon enough to yield conclusive results, said Dr. Emmanuelle Waubant, a neurologist at the University of California, San Francisco.

Waubant and her colleagues will present a case report about these patients’ illnesses at the American Academy of Neurology’s annual meeting in late April.

They are asking health care providers to be on the lookout for similar cases and send in samples from any patient exhibiting these symptoms.

Dr. Carol Glaser, chief of the Encephalitis and Special Investigation Section at the California Department of Public Health, said the state is aware of the paralysis cases but believes the risk to families is very low.

“We are evaluating cases as they are reported to us,” Glaser said in an e-mail to CNN. “We have not found anything at this point that raises any public health concerns.”

The poliovirus has been eradicated in the United States for more than 30 years.

Only three countries in the world are not yet free of the disease: Afghanistan, Pakistan and Nigeria, according to the World Health Organization.

Poliovirus is part of the Picornaviridae family, which also includes enteroviruses and rhinoviruses (better known as the common cold).

Between 1983 and 2005, 270 cases of enterovirus 71 were reported in the United States.

But none has resulted in a larger outbreak, despite the virus’s infectious nature.

“That’s the really odd thing,” Oberste said. “We see cases from time to time in the United States. Occasionally they’ll be severe. Basically it’s identical to what’s circulating in Asia … but it doesn’t cause the same big outbreak in disease. And we really don’t know why.”

The CDC is aware of the small cluster of cases in California but is not actively involved in an investigation, a spokesman told CNN.

Waubant and her colleagues don’t want to alarm anyone with their case report presentation; they’re simply seeking help in finding the cause of these seemingly connected cases.

“We would like to stress that this syndrome appears to be very, very rare,” one of Waubant’s colleagues, Dr. Keith Van Haren, said in a prepared statement.

Parents need to know that vaccination is key to preventing polio from returning to the United States, Glaser said.

While there is no vaccine to protect you from a non-polio enterovirus, washing your hands frequently and avoiding close contact with others who are sick can help.